1. Field of the Technology
The present technology relates to a developing device, an image forming apparatus, and a developer agitating and conveying method.
2. Description of the Related Art
A copier, a printer, a facsimile machine or the like is provided with an image forming apparatus which forms an image employing electrophotography. The electrophotographic image forming apparatus forms an electrostatic latent image on a surface of an image bearing member (photoreceptor) by a charging device and an exposure device, supplies a developer by a developing device to develop the electrostatic latent image, transfers a developer image on the photoreceptor onto a recording medium such as a recording paper by a transfer section, and fixes the developer image to the recording paper by a fixing device to form an image.
The developer supplied to the photoreceptor by the developing device is stored in a developer tank provided in the developing device. The developer stored in the developer tank is conveyed to a developing roller provided in the developing device. The developing roller rotates with the developer borne on a surface thereof to supply the developer to the photoreceptor. The developer is charged by frictional electrification in the course of being conveyed to the developing roller. The charged developer moves onto the photoreceptor from the developing roller by electrostatic force between the charged developer and the electrostatic latent image on the surface of the photoreceptor. In this way, the developing device develops the electrostatic latent image on the surface of the photoreceptor to form the developer image.
In recent years, in accordance with the increased process speed of an image forming apparatus and the reduction in size thereof, there is a demand for a developing device which is capable of rapidly and sufficiently charging a developer. For example, Japanese Unexamined Patent Publication JP-A 2004-272017 discloses a circulation type developing device which includes a first conveying path, a second conveying path, a first communication path and a second communication path formed by partition walls installed inside a developer tank, and a developer conveying section which conveys a developer through the first conveying path and the second conveying path in opposite directions. The developer conveying section disclosed in JP-A 2004-272017 has a structure of an auger screw including a rotation shaft member and a spiral blade spirally wound around the rotation shaft member, in which a plate-shaped member (fin) which is parallel with an axial line of the rotation shaft member is installed on the rotation shaft member.
The developer conveying section disclosed in JP-A 2004-272017 conveys the developer in an axial direction of the rotation shaft member by the spiral blade and moves the developer in a circumferential direction of the rotation shaft member by a main surface of the fin, to thereby frictionally charge the moving developer. However, in such a developer conveying section, there is a problem that the developer disposed between the spiral blade and a side surface of the fin is compressed and the compressed developer is not sufficiently frictionally charged. If the developer is not sufficiently charged, the image forming apparatus cannot form a high quality image.